While the aging of an ophthalmic solution may be viewed subjectively as a series of departures from original chemical and physical values, it is, of course, a much more complex matter clinically. The ultmate scales of solution aging also must take those factors into account that will affect the patient population and/or the lens in any significant way, e.g. toxicity, contamination, lens despoilation, loss of comfort. Since tissue tolerance and lens vulnerabilities are highly individualized, however, due to personal histories, genetics, sensitization, idiosyncracies), and the vast number of eye, lens, and care systemn combinations, the formulator (and through him, the clinician) must fall back on those chemical and physical departures as practical (first order) indices of risk
